1. Field of the Invention
The invention relates to a method for recording usage data of a card-operated device, the method comprising storing the usage data in a storage unit associated with the device. In particular, the invention relates to the secure storage of cost data in counters of public telephone sets of the type where a caller pays by means of a card, such as a so-called "chip" card. The invention also relates to recording usage data in general and cost data in particular for machines through which the purchaser pays by means of a card, such as, e.g., vending machines for sweets or for soft drinks, certain types of parking meters and stamp vending machines. In this context, the term "card" should be taken to refer to any type of card (or equivalent of a card) which enables the user to make use of the machine in question.
2. Description of the Prior Art
It is known in practice to equip pay telephone sets for public use ("pay phones") with a payment mechanism which settles payment by means of a card (e.g., phone card), such as a magnetic card or a "chip" card. On the card, a balance is stored in a magnetic strip or in a semiconductor memory. With each telephone conversation, the balance stored on the card is reduced, for example, with each metering pulse (billing pulse) of the telephone network or of the telephone set in question. This pulse may occur at a beginning of a minimum billing (charge) interval. Adjustment of the balance takes place, for a card having a semiconductor memory, by continually supplying the card with a pulse which causes a reduction of the balance, for example, by subtracting an amount from a stored value or by decreasing a content of an electronic counter internal to the card.
The number of telephone calls, the number of metering pulses and/or the amount of call charges can be recorded not only in the card, but also by a counter (or a different-type storage unit) associated with the pay phone itself. It is possible for such a counter not only to be located internally within the pay phone itself, but also to reside in a separate counting or recording device which is common to a number of pay phones but linked to the pay phones in question. Incidentally, a count of the charges is also kept in the telephone exchange to which a given pay phone in question is connected, but generally for other purposes. A counter, associated with a pay phone, of the type mentioned above may be used, not only, for example, for statistical purposes or for checking card balances, but also for settling call charges.
Such settling of charges may be carried out for various reasons. First, such charges may need to be shared with a commercial operator of a locality in which the pay phone in question is located, i.e., the commercial operator being paid part of the call charges. For example, it is standard practice in hotels and restaurants to impose a surcharge, which is ultimately paid to those establishments, for a caller's use of a pay phone situated there. Second, a settling of charges may be necessary with another telephone company if the caller makes use of a card of a telephone company different from that to which the pay phone in question is connected. The main instance that comes to mind here is the use of foreign cards, where it is necessary to settle the call charges with a foreign telephone company that carried a call made through the pay phone. Third, charges may need to be settled with a commercial operator of the pay phone itself--where that operator is not the telephone company to which that pay phone is connected but rather a different telephone company.
In the case of vending machines and the like, charges may be settled correspondingly with, for example, three parties; namely, the commercial operator of a locality where the machine is placed, the agency which has supplied the card, and a commercial operator of the machine. An example of a card-operated vending machine is described in German Patent Application DE-A-4 103 415. The vending machine described therein is provided with an additional card for recording operator revenues.
Card-operated devices are, however, subject to possible fraud, especially by mechanical and/or electronic manipulation of the card or the device. It is found that pay phones and vending machines are broken into with the possibility that the contents of their internal counters have been altered. There are also incidences of card balances being illegally increased so as to permit a card to be used for more and/or larger transactions than it should have been.
Consequently, reliable and fair settling of charges is obviously no longer possible in every instance. In the above-mentioned cases of the illicit use of a foreign card with a pay phone located in a certain commercially operated locality, the telephone company in question that owns the pay phone always loses revenue.
In conventional pay phones, each metering pulse or all the call charges are transmitted to the internal counter of the telephone set itself and subsequently to the card which has been inserted into the pay phone. The objective of doing so is to continually adjust, i.e., at each metering pulse, both the state of the counter of the pay phone and the balance of the card, thus permitting a subsequent balance of the card (and possible other usage data stored therein) to be checked. By means of suitable manipulations of the pay phone, the card could possibly be removed from the phone during an on-going telephone call, so that the call charges are no longer debited to the card. Although security procedures have been proposed which continually check the presence of the card, it is nevertheless not possible to guarantee that the charges recorded in the pay phone, as well as other data, will always track the data stored in the card. After all, metering pulses (or, in the case of a card equipped with a microprocessor, suitable instructions) could be transmitted to the card with the objective of reducing the balance on the card, but actually not reach the card owing to, for example, a technical fault or manipulation.
European patent application EP-A-0 185 365 discloses card-operated pay phones connected to a central computer, the computer providing data for verifying the authenticity of the card. The credit balance is written in the card at the end of a telephone call, but there is no guarantee that the actual balance so written is correct.
The publication W. Heberle and D. Lohner, "Offentliches Kartentelefon fur Wert- und Kreditkarten" (Public Card Telephone for Debit and Credit Cards), NTZ Nachrichtentechnische Zeitschrift, 1986 Vol. 39, No. 11 (Berlin) discloses card-operated pay phones in which the identity of the card is checked. Here, an "image" of a card is made. During a phone call, data recording is checked by repeatedly comparing this image with metering pulses received from an exchange. The identity of the image with the actual card can, however, not be guaranteed.
An electronic card-like based payment system for serving as an electronic surrogate for paper checks is disclosed in U.S. Pat. No. 4,529,870 (issued to D. Chaum on Jul. 16, 1985--hereinafter the "Chaum" patent). The system utilizes a card-like device and an interface, the latter being connected to an external financial system, such as a merchant's point-of-sale terminal or an on-line financial account system. The card-like device contains two basic stages: a secure (cryptographic) stage and a terminal stage--the latter effectively implementing a computer terminal to accommodate user interaction. In essence, for each payment and after suitable user authentication, this payment system obtains an electronic "check" number from the financial system. Once the check number has been received and the card-like device has debited its internal balance for the amount, the card-like device supplies payment instructions, including the payment amount and the electronic check number, via the interface, to the financial system in order to effectuate an electronic funds transfer to a payee. Inasmuch as this system relies on storing information, e.g., check number and payment amount, for each separate transaction to effectuate and later serve as proof of payment, this methodology is problematic with a variety of card-operated devices, such as pay phones and vending machines. Specifically, first, storing an individual record within the card-operated device of each and every different transaction effected therethrough necessitates a significant amount of memory, particularly where in the case of a pay phone each metering pulse (of which several will be involved in a typical long-distance call) will be viewed as a separate payment and hence as a different transaction. Second, if each separate charge, e.g., a metering pulse in a single telephone call, were to necessitate a separate "check", as ostensibly taught by the Chaum patent, then this would engender a significant amount of additional processing (and associated delay) in the card itself, the card-operated device and the financial system, thereby rendering this approach quite impractical for use in many card-operated devices, such as in a pay phone.